1. Field of the Invention
The present invention relates to a pick-up coil assembly for a magnetometer using a plurality of super-conducting quantum interference devices (SQUID's). The pick-up coil assembly according to the present invention is constituted by a plurality of pick-up coils arranged in an array configuration (for example, matrix) for enabling multi-channel measurement of magnetic field. The present invention is advantageously utilized for a digital SQUID magnetometer.
2. Description of the Related Art
A SQUID is widely used for detecting a weak magnetic field with very high sensitivity. That is, a SQUID can respond to a change in a weak magnetic field based on a quantum interference effect of the magnetic field. Accordingly, a SQUID is mainly utilized for, particularly, a high sensitivity magnetometer having a pick-up coil assembly as a magnetic sensor. A SQUID magnetometer is utilized, for example, in the medical equipment field to measure the weak magnetic field generated by the heart of a human body.
A detecting stage of the digital SQUID magnetometer (see, FIG. 19) is constituted by a superconductive pick-up coil for detecting a weak magnetic field from an object (human body), a superconductive input coil provided in the SQUID and magnetically coupled to the pick-up coil, and a superconductive feedback coil magnetically coupled to these coils. In general, the pick-up coil assembly is constituted by a plurality of coils (multi-channel), each coil corresponding to one channel, since it is necessary to simultaneously detect the magnetic field over a wide area on the object. For example, about 36 individual pick-up coils are necessary for diagnosing the heart.
In this case, since the pick-up coil assembly must detect a very weak magnetic field without dispersion of characteristics among pick-up coils, it is necessary to assemble the pick-up coil assembly with very high precision, particularly, structural precision so as to have high uniformity among coils.